Document Driven Development
Make sure the documents are well-formatted. You can use the simplest paragraphs, make it like prose, or just use a set of bullet points.
Use grammar tools checking grammar. Turn on the spellcheck option for editors.
Always remind yourself the goal of the document when writing and discussing. Clarify the goal and non-goal in the document. If you believe something is incorrect, use data and clear logic proving it.
Have the right people involved. Sometimes, you can also send out the documents to a wider range of people for reviewing so you can hear more voices.
It's okay to get a completely different solution at the end, but it needs to be the right solution and agreed by people. If people disagree, come back later with stronger cases.
List multiple solutions, each of which has pros and cons. Show which one of them is the best.
Make sure the solution in the document represent and advocate for the customer.
Think not just the problem domain and the solution set, but also the rest of the logic. Keep asking how and why during writing.